The involvement of highly reiterated DNA (hrDNA) sequences in chromosomal rearrangements is being studied utilizing the unique resources of the San Diego Zoo. Drawing on the vast reservoir of karyotypic diversity among mammals, closely related species with dramatically different karyotypes (e.g. the horse family, Equidae, the Indian muntjac, Muntiacus muntjak (2n equals 6 female, 7 male) and the Chinese muntjac, M. reevesi (2n equals 46) will be employed in studies of hrDNA sequence relatedness and cytological localization of hrDNA (including satellite DNAs) in chromosomal rearrangements. Of particular interest is the relationship between centromeric heterochromatin of the species with the higher diploid chromosome number to centromeric, telomeric and interstitial heterochromatin of the related species with a reduced diploid chromosome number. Cell lines derived from animals within the Zoo's collections and DNAs extracted from tissues obtained at necropsy will be used for these comparative studies. Heterochromatin of various species of interest will be examined utilizing cytological techniques (fluorochrome banding, G- and C-banding, silver staining for nucleolus organizer regions) and biochemical techniques (purification of satellite DNAs, reassociation kinetics, thermal stability of reassociated moleculaes, in situ hybridization, restriction endonuclease mapping, structural studies of satellite DNA-containing nucleosomes, and experimental induction of chromosome fusions and fissions).